1. Field of the Invention
This invention relates to catalysts, catalyst systems and to methods for their production and use in olefin polymerization.
2. Description of the Related Art
A catalyst technology has developed which provides for the modification and/or control over the properties and characteristics of a polymer. This technology principally involves the general field of transition metal catalysis. These catalysts can be referred to as bulky organo ligand transition metal catalysts. The bulky organo ligand contains a multiplicity of bonded atoms, preferably carbon atoms, forming a group which is cyclic and aromatic in nature. The bulky organo ligand may be a cyclopentadienyl ligand or cyclopentadienyl-derived ligand (collectively hereafter referred to as xe2x80x9cCpxe2x80x9d) which can be mono- or poly-nuclear. One or more bulky organo ligands are pi-bonded to the transition metal atom. The transition metal atom may be a Group 4, 5 or 6 transition metal. Other ligands may be bonded to the transition metal, such as a hydrocarbyl or halogen leaving group at least one of which is abstractable by a cocatalyst. The catalyst is derivable from a compound of the formula:
CpmMXn
wherein Cp is the bulky organo ligand, X is a leaving group, M is a transition metal and xe2x80x9cmxe2x80x9d and xe2x80x9cnxe2x80x9d are such that the total ligand valency corresponds to the transition metal valency. Preferably the catalyst is four co-ordinate such that the compound is ionizable by a cocatalyst to a 1+ valency state.
The ligands Cp and X may be bridged to each other and if two ligands Cp and/or X are present, they may be bridged to each other. The compounds, known as xe2x80x9cmetallocenes,xe2x80x9d may be xe2x80x9cfull-sandwichxe2x80x9d compounds having two Cp ligands which may be cyclopentadienyl ligands or cyclopentadienyl-derived ligands pi-bonded to the metal atom or xe2x80x9chalf-sandwichxe2x80x9d compounds having one Cp ligand which is a cyclopentadienyl ligand or cyclopentadienyl-derived ligand.
Generally, these bulky organo ligand catalysts are referred to as metallocene catalysts. Polymerization of olefins with metallocene catalysts requires their activation, such as by an alumoxane cocatalyst. Metallocene-alumoxane catalysts have been described in EP-A-0 129 368, published Jul. 26, 1989, U.S. Pat. Nos. 4,897,455, 4,937,299, 5,017,714, 5,057,475, 5,086,025 and 5,120,867. For instance, U.S. Pat. No. 5,057,475 and related U.S. Pat. No. 5,227,440 described a supported catalyst system that includes an inert support material, a Group 4 transition metal metallocene component and an alumoxane component.
EP-A-0 277 003 and EP-A-0 277 004, published Aug. 3, 1987, PCT International Publication WO 91/09882, published Jul. 11, 1991 and WO 92/0333 describe a Group 4 transition metal metallocene catalyst system that does not require alumoxane as an activator. The activator for the metallocene component described in these references is referred to as an ionic activator or a non-coordinating anion which comprises at least one moiety capable of abstracting a ligand other than the bulky organo ligand from the compound to produce a resulting cationic bulky organo ligand compound and an anionic activator compound. The ionic activator, which comprises a cation, irreversibly reacts with a ligand of a bulky organo ligand transition metal compound to produce a bulky organo ligand transition metal cation which combines with the anion of the activator to form an ionic pair. This ionic pair is the active catalyst.
The specifics of the structure of the cyclopentadienyl derived ligand, and any hetero-atom ligand when these ligands are bridged together in the transition metal compound can impart differing properties to the polymerization process and to the polymer thereby produced.
To date it seems that the Group 4 transition metals, namely, Ti, Zr and Hf have been the most studied and used transition metals for metallocene catalyst systems, especially for bis Cp catalyst systems xe2x80x94Cp2MX2xe2x80x94. Bis Cp catalyst systems are of particular interest for their ability to exert steric control over the insertion of comomers during the copolymerization of ethylene with a comonomer such as propylene, butylene, hexene or the like. In part it is believed that the bulky organo ligands of the full sandwich Cp2MX2 compound exerts a degree of steric and/or electronic guidance upon the path by which comonomer can approach the catalytically active metal site at which the polymer forms. Where xe2x80x9cnxe2x80x9d is the period of the Periodic Table of the Elements of the transition metal, bis Cp Group 4 transition metal compounds contain 16 electrons in the combination of the transition metal""s (n-1)d, (n)s and (n)p orbitals that participate in the formation of the molecular orbitals of the compound. Each pi-bonded Cp ligand contributes 5 electrons (2xc3x975=10) the group 4 transition metal contains 4 electrons and each to the two X ligands contribute 1 electron (2xc3x971=2) which sums to 16. Hence the molecular orbitals of the neutral Cp2Group 4 transition metal X2 compound are 2 electrons shy of that of the inert gas configuration of 18 electrons and can thus serve as active catalyst when the group 4 metal is in an ionic state. However, the effectiveness of such bis Cp transition metal compounds as catalyst declines significantly as their metal is changed out for the higher Group 5 and/or 6 transition metals. For example Cp2 Cr X2 would not be expected to be very catalytically active since it contains 18 electrons in its (n-1)d, (n)s and (n)p orbital shells which is the inert gas configuration.
It would be desirable to develop a bulky organo ligand for the formation of a wider range of bulky organo ligand transition metal compounds that would allow higher numbered group metals than the group 4 metals to be effectively used as catalyst components for olefin polymerization.
This invention is directed to cationic polymerization of olefins using catalysts comprising a Group 3, 4, 5, 6, 8, 9 or 10, or any subset thereof, transition metal cation composition wherein at least one ligand coordinated to the transition metal is a moiety comprising a cyclopropenyl structure. The neutral transition metal compound catalyst precursor is activated to a catalyst state by exposure to an activator composition which may be any of the heretofore known activator compositions such as alumoxane or a compatible non-coordinating anion (NCA). Hereafter a catalyst composed of such transition metal cation will be referred to as a xe2x80x9ccyclopropenyl transition metal catalystxe2x80x9d
Preferred cyclopropenyl transition metal derivatives include transition metals that are a mono- or bis- cyclopropenyl derivative of a transition metal. Preferred cyclopropenyl transition metal derivatives include transition metals that in their neutral state contain 16, 14, 12 and/or 10 electrons in the molecular orbitals derived from the (n-1)d, (n)s and (n)p orbitals of the transition-metal. After the cyclopropenyl ligand the remaining ligand structures of the transition metal composition can be like that of any mono- or bis- cyclopentadienyl (Cp) derivative of a Group 4, 5 or 6 transition metal here before known in the art to form an active metallocene catalyst system upon exposure to an activator composition.
With the cyclopropenyl transition metal compounds of this invention one may use a wider range of transition metals to form active catalyst systems that are activated by alumoxanes and/or non-coordinating anions.